[partition] Move SwapChoice to another namespace

- The choice of swap needs to be handled in more places,
   so make the enum available in the partition module core instead
   of just inside the choice page.

src/modules/partition/gui/ChoicePage.h

@@ -62,15 +62,6 @@ public:
         Manual
     };
 
-    enum SwapChoice
-    {
-        NoSwap,     // don't create any swap, don't use any
-        ReuseSwap,  // don't create, but do use existing
-        SmallSwap,  // up to 8GiB of swap
-        FullSwap,   // ensureSuspendToDisk -- at least RAM size
-        SwapFile    // use a file (if supported)
-    };
-
     explicit ChoicePage( QWidget* parent = nullptr );
     virtual ~ChoicePage();